POV-Ray : Documentation : Cylindrical
  POV-Ray 3.6 Documentation Online View Crackle Patterns Density_File Cylindrical

The cylindrical pattern creates a one unit radius cylinder along the Y axis. It is computed by: value = 1.0-min(1, sqrt(X^2 + Z^2)) It starts at 1.0 at the origin and decreases to a minimum value of 0.0 as it approaches a distance of 1 unit from the Y axis. It remains at 0.0 for all areas beyond that distance. This pattern was originally created for use with halo or media but it may be used anywhere any pattern may be used. Crackle Patterns Density_File

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